Methods and brake systems of the type named at the beginning are known from the related art. Hydraulically working brake systems apply a working pressure to wheel brakes, which is generated by a pump unit and transmitted via the brake fluid. Pump unit in this connection refers to any arrangement that is able to make a (fluid) pressure available, such as in particular dynamic or displacement pumps, for example piston or vane pumps, or also (master) brake cylinders or pressure accumulators. The brake fluid is transported through a brake line to the wheel brake. Between the wheel brake and the pump unit a valve is provided in the brake line which is operated to activate the wheel brake, in order to operate the wheel brake with the aid of the pressure generated by the pump unit.
If the brake line is damaged, for example by an accident, the brake fluid is able to escape from the hydraulic system. In the worst case, so much brake fluid escapes that it is not possible to build up sufficient pressure to initiate brake application.